Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session A19: Polymer Blends |
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Sponsoring Units: DPOLY Chair: Chinedum Osuji, Yale Room: B118-B119 |
Monday, March 15, 2010 8:00AM - 8:12AM |
A19.00001: Dynamics of Strongly Associating Polymer Blends Using Broadband Dielectric Spectroscopy Kevin Masser, James Runt In this study we investigate the dynamics of miscible polymer blends that preferentially form strong intermolecular hydrogen bonds. A random copolymer of p-(hexafluoro-2-hydroxyl-2-propyl)styrene [HFS] and 2,3-dimethylbutadiene [DMB] was synthesized for this study, as was an HFS homopolymer. HFS units are capable of forming strong intermolecular hydrogen bonds with complimentary species on a second miscible polymer, while minimizing the extent of intramolecular associations. The copolymer (or homopolymer) was blended with select homopolymers that form intermolecular hydrogen bonds of varying strength. Broadband dielectric relaxation spectroscopy is used to study segmental and local miscible blend dynamics, which are observed to vary significantly in the presence of hydrogen bonding. Fourier transform infrared spectroscopy was used to determine the degrees and strengths of hydrogen bonding present in the blends. [Preview Abstract] |
Monday, March 15, 2010 8:12AM - 8:24AM |
A19.00002: Solution self-assembly behavior of block copolymer blends with the same hydrophilic block but different hydrophobic blocks Jiahua Zhu, Ke Zhang, Karen Wooley, Darrin Pochan Novel micellar structures due to segregation of unlike hydrophobic domains trapped within the same micelle core have been produced via self-assembly of block copolymer blends in tetrahydrofuran/water solution. The blend is composed of two or more block copolymers with distinctive hydrophobic blocks but the same poly(acrylic acid) (PAA) hydrophilic block chemistry. By taking advantage of the complexation in the hydrophilic corona between the acid side chains of the PAA block and added organoamine molecules unlike hydrophobic blocks are trapped in the same micelle core and consequently, locally segregate. This segregation gives rise to a class of new multi-compartment micelle structures in which both the volume and shape of each compartment can be well controlled by changing the blending ratio, block length and kinetic pathway of micelle formation. The arrangement of hydrophilic PAA block and varied hydrophobic blocks within the micelles makes them potential templates for multi-functional composite nanomaterials by putting varied inorganic nanoparticles into targeting domains. Transmission electron, cryogenic transmission electron, and neutron scattering have been applied to characterize the assembled structures [Preview Abstract] |
Monday, March 15, 2010 8:24AM - 8:36AM |
A19.00003: Controlling co-monomer distributions in bulk and surface tethered random copolymers Lawrence Strickland, Jan Genzer, Carol Hall Tuning the chemical composition and co-monomer sequence distribution in random copolymers (RCPs) affects profoundly their physico-chemical characteristics. We present the results of discontinuous molecular dynamics (DMD) simulations of ``coloring'' reactions performed by reacting B species with A-type homopolymers to create A-\textit{co}-B copolymers both in bulk and tethered on an impenetrable, flat surface and discuss the effects of varying system temperature, chain length and surface density on copolymer blockiness. In bulk systems, decreasing the system temperature (i.e., reducing parent homopolymer solubility) results in RCP with a more random-blocky co-monomer character. Coloring of short homopolymers tethered to flat surfaces leads to copolymers whose blockiness is similar to those RCPs formed in the bulk. Increasing the chain length and/or increasing the surface density -- thereby increasing chain-chain interactions and restricting access to monomers near the surface -- results in RCPs with blocky (in some cases nearly diblock) monomer distributions. We also explore the means by which long blocky copolymers are formed as a function of the system temperature (relative to theta-temperature). [Preview Abstract] |
Monday, March 15, 2010 8:36AM - 8:48AM |
A19.00004: ABSTRACT WITHDRAWN |
Monday, March 15, 2010 8:48AM - 9:00AM |
A19.00005: Compatibilization of polystyrene and poly(dimethyl siloxane) with a star polymer having a $\gamma {\rm t}$cyclodextrin core and polystyrene arms C.M. Balik, A.E. Tonelli, Brad Busche Cyclodextrins (CDs) are cyclic starch molecules having a hollow central cavity which can be threaded by a polymer to form an inclusion compound. This characteristic is exploited in a new type of compatibilizer: a star polymer with a $\gamma {\rm t}$CD core and polystyrene (PS) arms. Atom transfer radical polymerization is used to grow and control the size of the PS arms from brominated initiator sites on $\gamma {\rm t}$CD. Solutions and thin films of PS and poly(dimethyl siloxane) (PDMS) are compatibilized by this CD-star. The mechanism of compatibilization involves threading of the CD core by PDMS and solubilization of the resulting ``slip-ring graft copolymer'' \textit{via} the PS star arms. Compatibilization of PS/PDMS in chloroform is visually observed when the initially turbid suspensions become clear solutions after addition of CD-star. Thin films spin-cast from these solutions exhibit a high degree of homogeneity and a nanoscale level of mixing. The solutions are characterized with NMR, dynamic light scattering and intrinsic viscosity measurements, and the thin films are characterized with optical and atomic force microscopy. Many different polymers are capable of threading the CD core, thus the same CD-star molecule could be used to compatibilize several different threading polymers with the same matrix polymer. [Preview Abstract] |
Monday, March 15, 2010 9:00AM - 9:12AM |
A19.00006: The Time Evolution of the Surface Segregation of Hyperbranched Molecules from a Linear Matrix Onome Swader, Mark Dadmun, Lian Hutchings, Richard Thompson Modification of a surface by the selective surface segregation of an additive in a mixture is a process with many commercial applications including biocompatibility, wettability, and anti-fouling in coatings. In a blend of branched and linear polymers, there exists an entropic driving force for the selective surface segregation of the branched polymer. Unfortunately, a systematic study of the impact of the branched copolymer structure on the dynamics and thermodynamics of this surface segregation is not currently available. Neutron reflectivity experiments that seek to fill this void have been completed and will be discussed. High molecular weight poly(styrene) (PS) hyperbranched molecules, hypermacs (HM) and dendrimacs (DM), with 10 \% HM or DM and 90 \% deuterated PS are the model systems studied. Reflectivity profiles for all blends were obtained as a function of annealing time from 30 minutes up to 48 hours. [Preview Abstract] |
Monday, March 15, 2010 9:12AM - 9:24AM |
A19.00007: Effect of \textit{Trans-Cis} Photoisomerization on Phase Equilibria and Phase Transition of Azobenzene Chromophore and Reactive Mesogenic Diacrylate Mixtures Namil Kim, Quan Li, Thein Kyu Photoisomerization-induced phase transition of neat liquid crystalline azobenzene chromophore (LCAC) and its mixtures with reactive mesogenic diacrylate monomer (RMDA) has been investigated experimentally and theoretically. Upon irradiation with UV light, the nematic phase of LCAC transformed to isotropic while the crystal phase showed the undulation on the surface (i.e., ripples). The phase transition temperatures and corresponding morphologies of the blends have been measured by means of differential scanning calorimetry and optical microscopy. Theoretical phase diagram of binary nematic and crystalline system was constructed by self-consistently solving the combined free energies of Flory-Huggins, Maier-Saupe, and phase-field theory. It displayed various coexistence regions such as nematic + isotropic (N$_{1}$ + I$_{2})$, crystal + isotropic (Cr$_{1}$ + I$_{2})$, crystal + nematic (Cr$_{1}$ + N$_{2})$, and crystal + crystal (Cr$_{1}$ + Cr$_{2})$ over the broad range of compositions and the single phase nematic (N$_{1}$, N$_{2})$ at the RMDA and LCAC rich compositions. The calculated liquidus lines were in good accord with the mesophase transition points. Of particular interest is that the \textit{trans-to-cis} isomerization of LCAC has led to suppression of N$_{1}$ + I$_{2}$ coexistence regions and disappearance of the N$_{2}$ phase of LCAC. [Preview Abstract] |
Monday, March 15, 2010 9:24AM - 9:36AM |
A19.00008: Concentration and Temperature Effects on the Micellization of Block Copolymers in a Homopolymer Matrix E. Pavlopoulou, K. Chrissopoulou, S.H. Anastasiadis, H. Iatrou, N. Hadjichristidis, G. Portale, W. Bras The micellization characteristics of a block copolymer / homopolymer blend above and near the critical micellization concentration (CMC) as well as below and near the critical micellization temperature (CMT) are measured with SAXS using a symmetric linear polystyrene-b-polyisoprene diblock in a low MW polyisoprene matrix. Both the core radius and the aggregation number are independent of concentration and temperature, implying that the micellar features depend only on the characteristics of the copolymer and the matrix. Just above CMC the volume fraction of micelles in the blends increases linearly with concentration, however this dependence becomes weaker as concentration further increases. The ``missing'' micelles are primarily attributed to additional copolymer chains that remain in the blends as unimers; that fraction increases with increasing concentration. The dissolution of micelles with temperature is manifested by a gradual decrease of the volume fraction of micelles in the blend with increasing temperature up to the CMT. Sponsored by NATO's Scientific Affairs Division, by the Greek GSRT and by the EU. [Preview Abstract] |
Monday, March 15, 2010 9:36AM - 9:48AM |
A19.00009: Micelle Formation of Diblock Copolymers in Thin Film Homopolymers and Homopolymer Blends Chelsea Chen, Peter Green A-b-B diblock copolymers, at very small concentrations, form micelles in a melt of homopolymer chains of type A or B. In the bulk, the critical micelle concentration, $\phi _{cmc}$, is a function of the symmetry of the copolymer chain and exhibits a strong dependence on $\chi $N, where $\chi $ is the interaction parameter and N is the degree of polymerization of the copolymer. We examined micelle formation in thin film mixtures of: (1) polystyrene-b-poly(2-vinylpyridine) (PS-b-PVP)/polystyrene (PS); (2) PS-b-PVP/ blend of PS and tetramethyl bisphenol-A polycarbonate (TMPC); and (3) polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA)/PS. The critical micelle concentration is found to be orders of magnitude larger than the bulk; it is a strong function of film thickness, the substrate/chain segment interactions and the interactions between the different polymeric segments in the system. [Preview Abstract] |
Monday, March 15, 2010 9:48AM - 10:00AM |
A19.00010: Micelle Formation in Diblock Copolymer/Homopolymer Films Jiajia Zhou, An-Chang Shi Diblock copolymers blended with homopolymers may self-assemble into micelles. When the diblock copolymer/homopolymer blends are confined between two flat surfaces, the shape of the micelles may differ from the bulk micelles when the thickness of the film is compatible to the micelle size. A real-space self-consistent field theory is used to study the micelle formation in diblock copolymer/homopolymer films. This study focuses on the effects of film thickness and surface selectivity. The results reveal that the spherical symmetry is destroyed by the film geometry whereas the top-down symmetry is broken by the surface selectivity. [Preview Abstract] |
Monday, March 15, 2010 10:00AM - 10:12AM |
A19.00011: Analytical course-grained description of a homopolymer melt as a liquid of soft colloidal chains Anthony J. Clark, M.G. Guenza Microscopic computer simulations of fluids of long polymers are greatly restricted by the limits of current computational power, and so course-grained descriptions accurate on molecular length scales are essential to extending the range of accessible systems. For some phenomena, particularly dynamical entanglement, descriptions that eliminate all internal degrees of freedom from the polymers are too drastic, as intermediate wavelength degrees of freedom are essential to the effect. Employing first-principles liquid state theory, we have developed a course-grained model for the intermolecular structure of melts of long homopolymer chains that maps each chain of hard-sphere monomers onto a chain of connected soft colloids. All dependence on system parameters is analytically expressed, so the results may be immediately applied to melts with different polymer and thermodynamic properties to calculate effective potentials between the soft-colloids on the chains, which can then be used to perform molecular dynamics simulations. These simulations capture the large wavelength structure of the system at greatly reduced computational cost, while still retaining enough internal degrees of freedom explicitly to describe phenomena that occur on length scales much larger than the monomeric units that comprise the chain, but shorter than the size of the molecule. [Preview Abstract] |
Monday, March 15, 2010 10:12AM - 10:24AM |
A19.00012: Nucleation in polydisperse polymer mixtures Dadong Yan, Shuanhu Qi The effect of polydispersity on nucleation in a metastable mixture of polydisperse polymer $A$ and monodisperse polymer $B$ is studied using self-consistent field theory. We adopt the continuous Schulz chain length distribution to describe the polydispersity of $A$ species. The results show that the free energy barrier, as well as many other properties of the critical nucleus, is sensitive to the polydispersity, especially in the highly polydisperse case. This should be attributed to the fact that longer chains have stronger tendencies towards nucleation. As a result, the distribution of the volume fraction as a function of chain length in the nucleus becomes different from that in the bulk. The chain length which corresponds to the maximum contribution to the volume fraction in the nucleus becomes larger than the number-average chain length. Meanwhile, the interface between the critical nucleus and the parent metastable bulk phase broadens. This phenomenon is obvious when the polydispersity is high. [Preview Abstract] |
Monday, March 15, 2010 10:24AM - 10:36AM |
A19.00013: The Entropic Rigidity of Circular Polymers Martin Bertrand, Martin Forget, B\'ela Jo\'os Thermal energy provides random motion to particles that leads to the well-known entropic force which favours the clumping of linear and circular molecules. We evaluate the entropic force which resists the radial dilation and subsequent twisting of circular polymers by developing mechanical models and performing molecular dynamics simulations. We find that dilating a looped chain is analogous to stretching its linear counterpart. We also find that the torque applied to an already dilated ring and the resulting twist are related by a linear relationship for a wide range of deformed configurations and, using this result, we can predict the angular fluctuations of such a macromolecule. [Preview Abstract] |
Monday, March 15, 2010 10:36AM - 10:48AM |
A19.00014: Microstructural Characterization of Plastic Bonded Explosives John Yeager, Daniel Hooks, David Bahr Plastic bonded explosives (PBX), a mixture of hard, anisotropic grains in a compliant matrix, represent an interesting case for understanding composite mechanical response and failure. PBX 9501 (0.95 cyclotetramethylene tetranitramine [HMX], 0.05 polymer binder) is relatively safe formulation of HMX, which is thought to be due to the high compliance of the binder. Crack formation between the crystals and the binder has been observed in this and many other systems and is usually the failure mechanism of PBX materials under mechanical strain. Thus the properties of the crystal-binder interface are important for development of failure models. The interfacial properties of PBX 9501 as well as an inert simulant have been characterized using several methods. Surface energies of several polymer binders and various crystallographic faces of HMX have been determined with a contact angle measurement technique, allowing for thermodynamic work of adhesion at the interface to be calculated. Surface roughness of the crystal faces has been measured with atomic force microscopy (AFM). PBX formulation methods are suspected to lead to a diffuse interface, but the nature of this interface has not previously been characterized in detail. Here, the coherence of the interface has been studied using tapping mode AFM for modulus contrast, and these findings are correlated with results from diffraction techniques. [Preview Abstract] |
Monday, March 15, 2010 10:48AM - 11:00AM |
A19.00015: Simulating the Effect of Flame Retardant Materials on Heat Diffusion in Polymers Joseph Ortiz, Arpon Raksit, Dilip Gersappe, Miriam Rafailovich Many commonly used polymers have low ignition temperatures, presenting the dangers of combustion and thermal degradation. Research is being done on the use of flame retardants, yet not much is known about the physics of heat loss due to these materials. Simulating the effect of flame retardants on the spread of heat throughout a polymer may provide a better understanding on how to effectively manipulate and make use of flame retardant materials. Using the lattice Boltzmann method, an algorithm that models the physics of fluid dynamics, a basic simulation of heat diffusion from a heat source to sink was implemented in three dimensions. The polymer and flame retardant material were incorporated into the system by implementing ignition within the particles of the polymer and by adding heat absorbing microscale filler particles within the polymer matrix. By manipulating the volume fraction of flame retardant particles, their ability to absorb heat, and their efficiency in removing heat from the system, different degrees of polymer combustion were simulated while polymer systems ranged from single polymer systems to multi-component blends. [Preview Abstract] |
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